The present invention relates to a semiconductor device, a power source unit, and an electrical device.
In a conventional power source unit, a conventional switching circuit may be provided for switching a plurality of power sources. Patent Reference 1 has disclosed an example of the conventional power source unit. According to Patent Reference 1, the conventional power source unit includes a power source supplied from a solar battery and a conventional switching circuit configured to selectively switch to a power source supplied from a primary battery. When a predetermined voltage is secured, the conventional switching circuit is configured to turn off the power supply from the primary battery and turn on the power supply from the solar battery. When a predetermined voltage is not secured, the conventional switching circuit is configured to turn on the power supply from the primary battery.
Patent Reference 1: Japanese Patent Publication No. 2006-10463
Patent Reference 2 has disclosed an example of a conventional wireless communication device. According to Patent Reference 2, the conventional wireless communication device includes a solar battery, a rechargeable battery, and a selection control unit. The selection control unit is configured to start with an internal capacitor, and to select one of the solar battery and the rechargeable battery.
In the conventional wireless communication device disclosed in Patent Reference 2, when a voltage value of the solar battery is greater than 1 V, the selection control unit selects the solar battery to supply power to a CPU (Central Processing Unit). When the voltage value of the solar battery becomes 2 V, the selection control unit selects the rechargeable battery to supply power to the CPU. Afterward, when the rechargeable value of the solar battery is less than 1 V, the selection control unit selects the rechargeable to supply power to the CPU. When the voltage value of the solar battery, which is measured repeatedly per specific constant time, is greater than 2 V, the selection control unit selects the solar battery to supply power to the CPU.
Patent Reference 2: Japanese Patent Publication No. 06-46538
When the conventional power source unit includes two types of batteries such as a battery formed of a primary battery and a secondary battery, and a solar battery, the conventional power source unit may be configured such that one of the battery and the solar battery having a higher output voltage is selected. In this case, when an output voltage of the battery is higher than an output voltage of the solar battery, the battery is selected even though the solar battery outputs the voltage sufficiently high to drive a system to which the conventional power source unit supplies power. Accordingly, the battery tends to be run out more quickly. In the conventional power source unit, when the solar battery is used more often, it is possible to prevent the battery from running out more quickly.
In view of the problems of the conventional semiconductor device described above, an object of the present invention is to provide a semiconductor device, a power source unit, and an electrical device capable of preventing a desired one of batteries constituting a power source from running out more quickly. Accordingly, it is possible to improve efficiency of the power source unit as a whole.
Further objects and advantages of the invention will be apparent from the following description of the invention.